Impact of Climate Variability and Change on the Surface Ozone Response to NOx Emissions Reductions.

Climate variability and change introduce a range of air quality outcomes for a given emissions policy. Quantifying this range helps us evaluate the likelihood of meeting air quality targets in an uncertain future climate. Using a global atmospheric chemistry model ensemble, we project how the ozone response to a 10% reduction in anthropogenic nitrogen oxides (NOx) emissions varies across three northern midlatitude source regions under two future climate scenarios. In Eastern North America and West-Central Europe, where ambient ozone is NOx-sensitive in the historical scenario, the magnitude of ozone reductions from reduced NOx is smaller under high warming relative to that under the historical scenario because of the dominant effect of increased soil NOx emissions. In North East Asia, where ambient ozone is NOx-insensitive in some areas in the historical scenario, the magnitude of ozone reductions from reduced NOx increases under high warming due to the dominant effect of enhanced HOx production. In North East Asia, these changes lead to a significant decrease in the frequency of days with ozone disbenefits from NOx reductions under the high-warming scenario relative to the historical scenario, while no statistically significant increase in ozone disbenefits is found for Eastern North America or West-Central Europe.